Biologists have studied the fly Drosophila melanogaster for decades. Given its status as a model organism (perhaps the model organism), one would think figuring out what its microbial fauna is would be a high priority. Yet remarkably little is known about its microbial fauna. Until now.A recent paper in Infection and Immunity characterizes the fauna of D. melanogaster. The authors goal was to figure out what the fauna is to use this fly as a model of intestinal disease. As far as I’m concerned, they have stumbled across something far more interesting.

The authors used a culture-independent approach: they PCR amplified and cloned the 16S rRNA gene (found in every bacterium, so it serves as a ‘barcode’), and then sequenced the 16S clones. The most interesting finding is that enterococci account for roughly a third of all clones, compared to mammals where they are common but at very low concentrations (~1% of the bacterial fauna, if that). Enterococcus faecalis was the most common just like in mammals. What was interesting is that the flies also had E. gallinarium, which has always been thought of as an ‘avian’ enterococcus (hence the name). For those of you who are Gram-negative fans, the most common Gram-negative bacterium was Enterobacter (which matches what we know about insects in general).

They also found that cytolysin, a toxin which causes disease in humans, also makes D. melanogaster sick (the flies were more likely to die). To boot, cytolysin producing enterococci also appear to have a competitive advantage over strains that don’t produce enterococci–just like in humans.